Time Resolved Carrier Dynamics in Ge-Based Heterostructures Grown on GaAs

While germanium (Ge) has long been an important player in microelectronics, strain-engineered Ge heterostructures have recently gained increased attention owing to the intriguing possibility of using strain to change the relative positions of the conduction band valleys and as a result, transitioning from an indirect to a direct gap material. Time-resolved pump-probe spectroscopy is an excellent tool to provide insight into the fundamental interactions, and microscopic dynamics of electrons, holes, phonons, and impurities. In this study, using complementary techniques of single color time-resolved differential reflectivity and two color time-resolved differential absorption, we investigated and gained insight into the effects of interfacial strain on carrier dynamics in several different Ge-based heterostructures. These include high-quality Ge films interfaced with InGaAs and AlSb grown on semi-insulating GaAs as the substrate. Our results are sensitive to the effects of both carrier recombination as well as electron inter-valley and hole inter-band scattering.